Al from Vernon, BC nails a 2x4 to the top of his extension ladder to be able to span across windows. We made a version of this setup that would work for any long ladder -- a 2x4 on the wall side, a shorter 2x4 on the other side, and two carriage bolts with wing nuts to sandwich it onto the top of any ladder, metal or wood.
We also saw a commercial stand-off that clamps onto a rung of any ladder, keeping the ladder itself off the wall. The stand-off we showed in the studio was a Crawford Ladder Stabilizer.